The results obtained so far indicate that the basic direction of investigation proposed in the original grant application can be pursued. Some of the specific projects to be undertaken are as follows: (1) to determine the patterns of acetylcholine sensitivity and alpha- Bungarotoxin binding on fibers prior to innervation, and examine how these patterns change following the initiation of synaptic transmission. (2) To study the anatomy of functions at each of the developmental stages, by marking specific fibers whose physiology is known and subsequently examining them with electron microscopy. (3) To investigate the cause of the abnormally long timecourse of the early end- plate potential. (4) To determine whether there is electrical coupling between muscle fibers at the time of innervation. (5) To determine when the number of axons synapsing on a single muscle fiber is reduced to the adult level. (6) To determine the effect of denervation of the limb on the physiology of newly-developed muscle fibers.